The turbine section of a turbine engine can include a rotor with discs on which a plurality of blades are attached. The blades extend radially outward from the discs and terminate in a region known as the blade tip. The blades are surrounded by a stationary support structure of the turbine, which can include an outer casing and blade rings. The space between the tips of the rotating blades and the neighboring stationary structure is referred to as the blade tip clearance.
For engine integrity, it is important that the tips of the blades do not rub against the nearby stationary structure. However, during transient conditions such as during engine startup or part load operation, it can be difficult to ensure that adequate blade tip clearances are maintained because the rotating parts (blades, rotor, and discs) and the stationary parts (outer casing, blade rings, and ring segments) thermally expand at different rates. As a result, blade tip clearances can actually decrease during engine startup or part load operation, raising concerns of blade tip rubbing. Thus, there is a need for controlling blade tip clearances when the engine operates under transient conditions such as during engine startup and part load.